Developmental changes in the electrically excitable membrane of a clonal rat skeletal muscle cell line have been studied. Since further detailed studies are required to understand precisely what is happening in the membrane during differentiation, the voltage clamp method is going to be applied to this system. Previous work has shown that synapses are formed between the clonal muscle cell line (L6) and explants of fetal rat spinal cord. Several characteristic features were found in this newly formed synapse. Characterization of these synapses and their development using electrophysiological and electron microscopic techniques will be continued. As a long term project, synapse formation between clonal cell lines will be sought.